1. Field of the Invention
The present invention relates to a double-sided pressure-sensitive adhesive sheet used for sticking and fixing a touch panel to a display surface of a display device, and a method for sticking and fixing a touch panel to a display device.
2. Related Art
A large market for mobile communication terminals (e.g., mobile telephone terminals such as cellular phones and PHS machines, and PDA terminals) have been formed in recent years. The main technical streams for the mobile communication terminals are directed to reduction in thickness, reduction in weight, reduction in power consumption, increase in definition, increase in luminance, and so on. Particularly from the point of view of reduction in weight and breaking prevention, a touch panel used as an input device in a PDA has begun to shift from a touch panel having a configuration (F/G type) in which a transparent electrically conductive plastic film [e.g., a transparent electrically conductive plastic film such as a transparent electrically conductive polyethylene terephthalate film (electrically conductive PET film) having a polyethylene terephthalate film as a base and an electrically conductive layer such as ITO (Indium Tin Oxide) formed on one surface of the polyethylene terephthalate film] is stuck to an electrically conductive glass sheet by a pressure-sensitive adhesive agent as shown in FIG. 3 to a touch panel having a configuration (F/F/P type) in which two transparent electrically conductive plastic films (such as electrically conductive PET films) having electrically conductive layer-forming surfaces disposed opposite to each other are stuck to a transparent substrate of polycarbonate or the like as a reinforcing member through a transparent pressure-sensitive adhesive agent as shown in FIG. 4. Incidentally, the touch panel is stuck and fixed to an LCD module through a pressure-sensitive adhesive layer shaped like a picture frame on the LCD module.
FIG. 3 is a schematic sectional view showing an example of the related-art F/G type touch panel. FIG. 4 is a schematic sectional view showing an example of the related-art F/F/P type touch panel. In FIGS. 3 and 4, the reference numeral 11 designates a double-sided pressure-sensitive adhesive tape; 51, an F/G type touch panel; 51a, an electrically conductive PET film on the upper side; 51b, an electrically conductive glass sheet on the lower side; 51c, an adhesive layer; 51d, a silver paste layer; 52, an F/F/P type touch panel; 52a, an upper electrically conductive PET film; 52b, a lower electrically conductive PET film; 52c, an adhesive layer; 52d, a silver paste layer; 52e, a double-sided pressure-sensitive adhesive tape; 52f, a reinforcing plate; 6, an LCD module; 7, a backlight unit; and 7a, a double-sided pressure-sensitive adhesive tape.
In the F/F/P type configuration as shown in FIG. 4, however, two air interfaces are formed between the electrically conductive plastic films 52a and 52b of the touch panel 52 and between the touch panel 52 and the LCD module 6. For this reason, there arises a problem that light loss due to reflection is large. There also arises a problem that the touch panel 52 is thick. These problems are considerably serious against the stream of reduction in power consumption, increase in luminance, reduction in thickness, and so on.
A touch panel having a configuration (F/F type configuration) in which electrically conductive layer-forming surfaces of two transparent electrically conductive plastic films are disposed opposite to each-other as shown in FIG. 5 has been proposed newly on such circumstances. FIG. 5 is a schematic sectional view showing an example of the related-art F/F type touch panel. In FIG. 5, the reference numeral 12 designates a double-sided pressure-sensitive adhesive sheet; 5, a touch panel; 5a, an upper electrically conductive PET film; 5b, a lower electrically conductive PET film; 5c, an adhesive layer; and 5d, a silver paste layer. Incidentally, the reference numerals 6, 7 and 7a designate an LCD module, a backlight unit and a double-sided pressure-sensitive adhesive tape respectively like FIG. 3 and FIG. 4.
In the F/F type configuration, air interfaces can be reduced more greatly, so that the thickness of the touch panel 5 can be reduced. When the related-art double-sided pressure-sensitive adhesive sheet 12 (such as a pressure-sensitive adhesive tape) is used, the touch panel 5 and the LCD module 6 are, however, bonded to each other so firmly that they cannot be mended after they have been bonded to each other once. Hence, the LCD module 6 and the touch panel 5 cannot be discarded if they are stuck to each other improperly. In addition, transparency is low. Hence, there is a problem that light transmittance as a whole is reduced even in the case where reflection loss is reduced due to reduction in the air interfaces.